Peculiarities of influence of parameters of the post-deformation heat treatment and chemical composition of steel on the formation of actual size of grain

Ingots and continuous cast billets are hot deformed when the steel is in the austenitic state. The temperature range of steel deformation in industrial conditions is quite diverse (1 080…1 200 °C). For each steel the heating temperature is determined taking into account its chemical composition and propensity to grow austenitic grains. Plastic deformation of metals and alloys in the austenitic state is accompanied by two competing processes: an increase of the density of dislocations, which causes the hardening, and rebuilding of the microstructure and substructure (dynamic softening). In the intervals between reductions the steel partially restores its structure, therefore the formation of the final microstructure is the result of the total number of reductions at different temperatures and pauses between them, that is, it depends on static and dynamic processes. Purpose. To establish the peculiarities of the influence of the parameters of post-deformation heat treatment and the chemical composition of carbon steel on the formation of the size of pearlite grains in the structure of rolled products. Results. The established specific features of the influence of post- deformation heat treatment parameters and chemical composition indicate that when the air cooling temperature is decreased for high carbon steel C82DV, along with dispersion hardening, grain-boundary hardening can develop, which is caused not only by the release of carbides or nitrides, but also by slowing down the recrystallization processes. At the same time, when steel C82DCr is doping with chromium in an amount up to 0.27 %, hardening occurs due to the solid-solution mechanism (carbides and chromium nitrides are not detected). It is shown that the study of the features of the formation of the grain structure and mechanical properties of high carbon steels, including those doped with carbide-forming elements (vanadium and / or chromium), should be carried out from temperatures of at least 1 040 °C, at which the barrier mechanism does not significantly affect the migration of austenite grain boundaries and the formation of austenite structure before the start of continuous air cooling of wire rod.